History of Molecular Genetics
Friedrich Miescher
• In 1869 extracted a viscous white substance
from the nucleus of a cell
• Substance was slightly acidic and rich in
phosphorous and nitrogen
• Named it nuclein because it was found in the
nucleus
Frederick Griffith
• In 1920s tried to develop a vaccine against
pneumonia
• Discovered transformation
Joachim Hammerling
• In 1930s studied one-celled green alga
Acetabularia to determine the location of DNA
within the cell
Oswald Avery, Maclyn McCarty and
Colin McLeod
• In 1944 Avery and colleagues continued the work
of Griffith
• Ruptured heat-killed encapsulated cells to release
their content. Each component (DNA, RNA,
protein) was isolated and tested for transforming
ability
• Determined that protein is not the hereditary
material but instead DNA is the material of which
genes and chromosomes are made
Erwin Chargaff
•In 1950s studied DNA in many
different organisms
•The proportion of Adenine in a
DNA molecule is equal with to that
Thymine, and the proportion of
Guanine is equal to that of
Cytosine
• Found that the composition of DNA varies from
one species to another, in particular in the relative
amounts of A, G, T, and C bases
• Helped lead to the discovery of the double helix
structure of DNA
Alfred Hershey & Martha Chase
• In 1952 found virus
infects a bacterial host by
attaching to the surface
of the cell and injecting
its DNA into the cell. This
produced 1000s of new
viruses which burst out of
the cell, resulting in cell
death
• Results: only the DNA
(rich in phosphorus) from
the virus, not the protein
(rich in sulfur), enters the
bacteria to direct the
synthesis of new viruses
(reproduction)
Rosalind Franklin
• In 1953 with her student Raymond Gosling,
discovered that there were two forms of DNA
– when wet, the DNA fibre became long and thin
– when it was dried it became short and fat
• Discovered that the sugar-phosphate backbone of
DNA lies on the outside of the molecule, not the
inside as was previously thought
• Could not discover from her data was how the bases
paired on the inside of helix, for which James Watson
and Francis Crick had the answer
James Watson & Francis Crick
• In 1950s put the last piece
of DNA structure together
from a variety of sources
including Franklin and
Chargaff
– Rosalind Franklin was friendly
with Watson & Crick, and
communicated regularly with
them until her life and career
were cut short by cancer in
April of 1958, at the age of 37
Matthew Meselson & Franklin Stahl
• In 1958 discovered that DNA replication is semiconservative: ½ of the double helix is old; ½ is
new)
Human Genome Project
• $3 billion project began in 1990 by the United States
Department of Energy and the U.S. National Institute of Health
and was expected to take 15 years
• Comprised of 1000s of geneticists from around the world
• A working draft of the genome was announced in 2000 and a
complete one in 2003, with further, more detailed analysis still
being published
• The ultimate goal was to “understand the human genome” and
gain “knowledge of the human as necessary to the continuing
progress of medicine and other health sciences”
• Main findings:
– over 3 billion base pairs
– approx 30,000 genes in human beings, the same range as in mice and
roundworms
– 98% of the genome is “junk” DNA
The Secret of Life - Discovery of DNA
Structure
• ..\..\..\..\Videos\Teaching\The Secret of Life -Discovery of DNA Structure.avi
– Handout: Questions on the video
The Secret of Life - Discovery of DNA
Structure
A1 Before WWII focus of genetics was on military
needs. After WWII focus shifted to exploring the
basis of life
A2 Proteins
A3 Watson was trained as a zoologist and enjoyed
bird watching. Crick was a physicist
A4 Linus Pauling completed with Watson & Crick.
Rosalind Franklin collaborated with Watson &
Crick
Homework
• Pg 209 Questions 4, 5 and 6